This invention relates to a MOS-bipolar device and, more particularly, to a Clustered Insulated Gate Bipolar Transistor (CIGBT) and a process for fabrication thereof.
Traditionally, power Metal Oxide Field Effect Transistors (MOSFETs) have been used in low to medium power applications. However, it has been found that Insulated Gate Bipolar Transistors (IGBTs) enable better switching performance in such applications due to their lower on-state power loss and higher current densities. The power ratings of IGBTs are slowly increasing and they are envisaged to replace thyristors in medium power applications such as High Voltage Direct Current (HDVC) inverter systems and traction drive controls.
MOS Gated Thyristor (MGT) devices have been identified as a promising alternative to transistor based devices as they exhibit a lower forward voltage drop and improved current densities. The CIGBT described in International Patent Application No. WO01/18876 is a MOS gated thyristor device that exhibits a unique self-clamping feature that protects cathode cells from high anode voltages under all operating conditions. The self-clamping feature also enables current saturation at high gate biases and provides low switching losses, and its low on-state voltage and high voltage blocking capabilities make the CIGBT highly suitable as an alternative to the IGBT.
It is an object of the present invention to provide a cathode cell structure, and method of fabricating the same, using CIGBT technology.